Opening microwave antenna having parasitic tuning slots and tuning plates to adjust effective phase center



y 1962 A. E. RATKEVICH OPENING MICROWAVE ANTENNA HAVING PARASITIC TUNING SLOTS AND TUNING PLATES TO ADJUST EFFECTIVE PHASE CENTER Flled March 31, 1958 Fig! INVENTOR. ADAM E. RATKEVICH Mama United States Patent Qfl ice 3,046,551 Patented July 24, 1962 The present invention relates generally to microwave antennas and more particularly to a receiving antenna feed.

The primary object of this invention is to provide a microwave antenna feed primarily for use in scanning systems as, for example, at the effective focus of a parabolic receiver antenna to receive signal energy from the antenna at four individual feed elements, arranged to provide sequential scanning ofthe antenna in four directions.

Another object of this invention is to provide a receiving antenna feed in which the individual feeds are large enough for efiicient signal transmission and thus are physically spaced from each other, yet their effective phase centers are brought closer together by novel means.

Still another object of this invention is to provide a four-feed plate having improved isolation between feeds, so that the effective phase centers are relatively independent of mismatches in the antenna system.

Finally, it is an object to provide an antenna feed of the aforementioned character which is compact, has no moving parts and requires a minimum of maintenance.

With these and other objects definitely in'view, this invention consists in the novel construction, combination and arrangement of elements and portions, as will be hereinafter fully described in the specification, particularly pointed out in the claims, and illustrated in the drawing which forms a material part, of this disclosure, and in which:

FIGURE 1 is a front elevation view of the antenna feed;

FIGURE 2 is a sectional view taken on the line 2--2 of FIGURE 1; and

FIGURE 3 is a sectional view taken on the line 33 of 'FIGURE 1.

Similar characters of reference indicate similar or identical elements and portions throughout the specification and throughout the views of the drawing.

Referring now to the drawing in detail, one practical embodiment of the invention is represented as a thick, circular plate 10, or the equivalent, having suitable means for attachment, such as a continuous radially extending flange 12 with a fiat rear face 14. The flange 14 may be provided with a plurality of screw threaded holes 16, or the like, for attachment of the device to an antenna assembly.

The plate has four rectangular openings definin feeds extending completely through its thickness and arranged in pairs symmetrically about the center of the plate. For convenience, the feeds will be referred to as the upper and lower feeds 18 and 20, respectively, and the left and right feeds 22 and 24, respectively. Minor variation may be resorted to but as illustrated the upper and lower feeds 18 and 20 are longitudinally opposed, their adjacent ends being separated only by a narrow web 26 of the plate 10. The left and right feeds 22 and 24 are disposed in spaced relation on opposite sides of the feeds l8 and 20 and are spaced symmetrically about the center of the plat-e 10, all four feeds being parallel to each other and their centers may be considered as being arranged substantially in a diamond pattern.

The physical dimensions of the feeds 18 to 24 are identical and their dimensions bear a definite relationship to the wavelength of the signal used, as will be more defi- I nitely specified hereinafter, the feeds having a length which allows efiicient transmission of signal energy without the necessity for dielectric inserts, the use of which is well known in the art. By making the feeds relatively large 1n this manner, the physical feed centers are necessarily spaced apart a certain distance. For efiicient antenna operation it is desirable to have the feed centers as close together as possible within certain limits according to the particular antenna system and the type of signal being handled. 4

The upper and lower feeds.18 and 20 are provided with tuning plates 28, which are flat, generally rectangular plates slightly wider than the feeds, and are mounted on the front face of the plate 10 overlapping the outer ends of said feeds. These tuning plates 28 may be secured to the plate 10 in any suitable manner and by partially closing the upper and lower feeds 18 and 20 at the opposed outer ends, the effective phase centers of these feeds are moved inwardly toward each other, with out actually reducing the physical size of the feeds.

The left and right feeds 22 and 24 have their effective phase centers moved together by means of parasitic tuning slots 32, which are slightly spaced from and parallel to the opposed outer edges of said feeds, the parasitic slots being slightly longer than the feeds themselves and a quarter of a wavelength deep, thus extending onlypartially through the plate 10. These parasitic slots 32 have the dual function of isolating the feeds and also moving the effective phase centers of the left and right feeds 22 and 24 closer together. The theory of operation of such slots need hardly be here reviewed. As an example of the dimensional relationship of the feed elements, in one particular antenna the feed slots themselves are each .510 inch long and .187 inch wide, while the parasitic slots 32 are .64 inch long, .0312 inch wide and a quarter of a wavelength deep. These dimensions would, of course, vary with the wavelength of the signal 7 energy being used.

The received signals are fed into suitable waveguides,

indicated in dash line at 34, which are connected to a' scanning device to scan the feeds 18 to 24 sequentially.

, Such a scanning device is described in my copending ap- It will be obvious that all said objects are amply achieved by this invention. It is understood that minor variation from the form of the invention disclosed herein may be made without de- 7 parture from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.

I claim:

1. A microwave receiving antenna feed, comprising: a

generally flat plate having a plurality of generally rectangular'openings defining microwave conducting feeds extending through the plate; said feeds being arranged in two pairs, one of said pairsbeing longitudinally opposed and closely spaced about a common center, the other of said pairs being laterally opposed and spaced on opposite sides of said first mentioned pair about the common 1 center; a pair of tuning plates fixed to one face of said plate at the outer ends of said first pair of feeds and partially covering the same, whereby the effective phase 1 3 centers of said first pair of feeds are moved toward the common center; a pair ofparasitic tuning slots in said one face and extending partially through said plate and being spaced from and parallel to the outer edges of said second mentioned pair of feeds.

2. The combination of claim 1 and including a wave guide connected to each said feed, whereby the received microwave energy may be applied to a utilization device.

3. The combination of claim 1 wherein said parasitic tuning slots are slightly longer than said outer edges.

4. A microwave receiving antenna feed, comprising: a generally flat plate having a plurality of generally rectangular openings defining microwave conducting feeds extending through the plate, said feeds being arranged in two pairs, one of said pairs being longitudinally opposed and closely spaced about a common center, the other of said pairs being laterally opposed and spaced on opposite sides of said first mentioned pair about the common center; and a pair of parasitic tuning slots in one face of said plate and extending partially through said plate and being spaced from and parallel to the outer edges of said second mentioned pair of feeds.

5. A microwave receiving antenna feed, comprising: a generally flat plate having a plurality of generally rectangular openings defining microwave conducting feeds extending through the plate, said 'feeds'being arranged in two pairs, one of said pairs being longitudinally opposed and closely spaced about a common center, the other of said pairs being laterally opposed and spaced on opposite sides of said first mentioned pair about the common center; and a pair of parasitic tuning slots in one face of said plate and extending partially through said plate and being spaced from and parallel to the outer edges of said second mentioned pair of feeds, said slots being slightly longer than said outer edge of said second mentioned pair of feeds.

6. The combination of claim 5 wherein said parasitic tuning slots have a depth of a quarter of a wavelength of the microwave that is being received.

References Cited in the file of this patent UNITED STATES PATENTS 2,461,005 Southworth Feb. 8, 1949 20 2,557,951 De Rosa et al. June 26, 1951 2,574,433 Clapp Nov. 6, 1951 FOREIGN PATENTS 1,080,702 France June 2, 1954 

